The present invention relates to a process for continuously hydrolyzing ethylene-vinyl acetate copolymer, and more particularly to a process for continuously preparing a high hydrolyzed ethylene-vinyl acetate copolymer by hydrolyzing an ethylene-vinyl acetate copolymer in the presence of an alkaline catalyst in a methanol medium.
There hitherto has been proposed a process for continuously preparing a high hydrolyzed ethylene-vinyl acetate copolymer as disclosed in the Japanese Examined Patent Publication (Tokkyo kokoku) No. 14958/1968, in which an ethylene-vinyl acetate copolymer is hydrolyzed by feeding a methanol solution of a copolymer including ethylene and vinyl acetate as main components and an alkaline catalyst into the upper portion of a tower reactor, while blowing a methanol vapor into the tower reactor to carry out an effective reaction in the tower reactor and removing a methyl acetate vapor together with a methanol vapor out of the tower reactor. In accordance with the above-mentioned Patent Publication, there is disclosed that an amount of the alkaline catalyst is decreased into 1/3 to 1/2 and a reaction time is decreased into 1/5 to 1/3 in comparison with a conventional batch wise process. A fairish amount of sodium acetate, however, is included in the resulting hydrolyzed ethylene-vinyl acetate copolymer, and a washing and removing step of a sodium acetate is needed after a hydrolyzing step. There has been proposed a process for hydrolyzing ethylene-vinyl acetate copolymer as described in the Japanese Examined Patent Publication No. 38558/1972, in which an ethylene-vinyl acetate copolymer is hydrolyzed by feeding a methanol solution of copolymer including ethylene and vinyl acetate as main components into an upper portion of tower reactor while blowing a methanol vapor into the tower reactor to carry out an effective reaction in the tower reactor and removing methanol vapor and methyl acetate vapor out of the tower reactor; and, in that case, a catalyst to be added into a reaction system is divided into two or more parts in order to feed them not only into the upper portion of a tower reactor but also into the middle portion of tower reactor. In accordance with this process, the amount of an alkaline catalyst is decreased into 1/5 to 1/20, and further, a washing and removing step after hydrolysis can be reduced in comparison with the process in the above-mentioned Japanese Examined Patent Publication No. 14958/1968.
But it is impossible to omit the step for washing and removing sodium acetate.
The object of the present invention is to provide an improvement of the above-mentioned process in the Japanese Examined Patent Publication No. 38558/1947.
A further object of the invention is to provide a process for preparing high hydrolyzed ethylene-vinyl acetate copolymer by using a little amount of alkaline catalyst.
Another object of the invention is to provide a process for preparing a non-colored highly hydrolyzed ethylene-vinyl acetate copolymer.